I train low-volume, and think both the 20 rep set and the 4 sets of 5 are needed for continued growth. However, I would never do 4 working sets of anything on any one lift. I typically alternate every other week with this. In the 20 rep example, I might do two or three warm-up sets on squats and then hit one crazy set of 20 with a weight I know I can do only 15 to 18 times on a good day. After that, I'm off to the next lift.
Disclaimer: I do not, nor have I ever, condondone anything SSidiotSS says or does. He is a complete fool and anyone reading his threads should proceed with caution, knowing the statements made are most likely not only false, but counterproductive in nature.